340 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 



degrees above the horizon, and only 4 per cent when the sun was at an 

 altitude of 50 degrees. When the sky was light blue and cloudless the 

 absorption was greater than when it was deep blue. 1 Of course, these 

 experiments refer to the whole thermal solar energy, and there is at 

 present no record of the varying amounts of absorption of dark heat 

 only, or of the varying loss by radiation from an object on the surface 

 of the earth in different conditions of the unclouded sky. 



SOUND IN AIR. 



Experiment has still to determine the rate of propagation of sound 

 in air at different temperatures in average atmospheric conditions at 

 those temperatures indifferent countries; the rate of propagation for 

 intense compared with feeble sounds; the rate for notes of widely dif- 

 ferent pitch, and what sounds may be most effective at long distances 

 to the ear and to recording instruments. It is conceivable that instru- 

 ments may be constructed which would enable messages to be sent by 

 the voice or otherwise through long distances of air. Converging 

 lenses of gas have been constructed for focusing sounds, and similar 

 ones might perhaps be utilized if made on a large scale. 



The homogeneity and discrepancy or heterogeneity of the atmos- 

 phere have been ascertained to be very important in the transmission 

 and arrest of sound waves; it seems frequently to be impossible, with 

 our present knowledge, to distinguish a good from a bad hearing day. 

 The air is often divided, apparently, into larninee or divisions of differ- 

 ent density, humidity, etc., which stops waves of sound and may even 

 reflect them loudly, though transparent. All these points deserve 

 further elucidation, and are of consequence for maritime and military 

 and naval purposes. They may also serve, with other prognostics, for 

 the forecast of weather. The echoing power of clouds of different 

 kinds is not well made out. The practicability of production of sounds 

 in a dense medium, such as air under pressure or in carbonic acid gas, 

 in order to increase its intensity, is worth investigation. 



POSITION OF THE PLANETS, SUN SPOTS, AURORJE, WEATHER, AND 



CROPS. 



Investigation of the reality of connection between the position of the 

 planets, the number and extent of solar spots and prominences, terres- 

 trial magnetic disturbances and auroras, cycles of weather, and agri- 

 cultural crops. 



AEROLITES. 



The number of aerolites, or shooting stars, which enter the atmos- 

 phere daily; their size, weight, and any effect they may have on the 

 upper atmosphere. The possibility of any general sky illumination by 

 the passage of small particles, compared to fine dust. 



l Rendiconti del Reale Iiistituto, Lombardo, 1894. 



